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1 #+title: Notes for "Special Topics in Computer Vision"
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2 #+author: Robert McIntyre
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3 #+email: rlm@mit.edu
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4 #+description:
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5 #+keywords:
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6 #+SETUPFILE: ../../aurellem/org/setup.org
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7 #+INCLUDE: ../../aurellem/org/level-0.org
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8 #+babel: :mkdirp yes :noweb yes :exports both
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9
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10 * Fri Sep 27 2013
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11
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12 Lambertian surfaces are a special type of Matt surface. They reflect
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13 light in all directions equally. They have only one parameter, the
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14 amount of energy that is absorbed/re-emitted.
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15
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16 [[../images/adelson-checkerboard.jpg]]
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17 #+caption: Lol checkerboard illusion.
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18
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19 Look into Helmholtz' stuff, it might be interesting. It was the
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20 foundation of both vision and audition research. Seems to have took
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21 a sort of Baysean approach to inferring how vision/audition works.
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22
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23 - Homomorphic filtering :: Oppenhiem, Schafer, Stockham, 1968. also
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24 look at Stockham, 1972.
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25
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26 Edwin Land was Adelson's hero back in the day. He needed to create a
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27 color photo for the Polaroid camera. In order to process for
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28 automatic development of film, he had to get a good approximation for
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29 the illumination/reflectance decomposition that humans do, which he
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30 called Retinex.
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31
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32 Cornsweet square wave grating is cool.
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33
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34 - Retinex :: use derivatives to find illumination. Sort of
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35 implicitly deals with edges, etc. Can't deal with
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36 non-lambertian objects.
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37
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38
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39 Adelson introduces the problem as an "inverse" problem, where you
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40 try to "undo" the 3-d projection of the world on your retina.
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41
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42 On the functional view of vision : "What it takes" is to build a
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43 model of the world in your head. The bare minimum to get success in
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44 life is to have a model of the world. Even at the level of a single
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45 cell, I think you still benefit from models.
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46
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47 Spatial propagation is ABSOLUTELY required to separate embossed
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48 stuff from "painted" stuff. Edges, likewise, MUST have spatial
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49 context to disambiguate. The filters we use to deal with edges must
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50 have larger spatial context to work, and the spatial extent of this
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51 context must be the ENTIRE visual field in some cases!
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52
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53 ------------------------------------------------------------
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54
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55 ** Illumination, shape, reflectance all at once
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56
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57 What if we tried to infer everything together? Some images are so
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58 ambiguous it requires propagation from all three qualities to
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59 resolve the ambiguity.
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60
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61 Brain has a competing painter, sculptor, and gaffer which each try
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62 to "build" the things in the world. There is a cost to everything
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63 such as paints, lights, and material, and then you try to optmize
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64 some cost function using these primitives.
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65
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66
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67 Horn, technical report, 1970
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68
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69
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70
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71 * Fri Oct 4 2013
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72
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73 Student report. Talked about how you capture the appearance of a
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74 grape. It's actually quite compicated, involving gloss, spatial
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75 context, etc.
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76
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77 Turbosquid seems interesting. They sell 3D models of stuff.
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78
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79 BRDF -- bi-directional reflectance distribution function this shows
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80 how a surface will behave given lighting conditions. Lambertian is a
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81 simple parameterized instantiation of this.
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82
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83 BSSRDF -- (SS = subsurface) 3D analogue of BRDF
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84
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85 What would the 3D analiogue of texture be?
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86
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87 (a : b : c) as (a + b + c : b + c : c) <-- this is just the golden
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88 ratio again!
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89
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90 CURET BTF Database lol what's this
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91
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92 This student went and gathered 1000 images of different large
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93 objects made of different materials. The images were gathered off of
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94 Flikr.
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95
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96
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97
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98
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